Abstract
Sentinel-2 MSI and Senitnel-3 OLCI are two visible imagers contributing to the European Copernicus Earth Observation program. Both instruments are periodically calibrated using on-board Sun diffusers. OLCI has two Sun diffusers (nominal and reference diffuser), while MSI has only one. OLCI uses a shutter to perform dark signal calibration, while MSI relies on nigtht-time acquisitions over the Ocean. Finally, OLCI has a coloured diffuser for spectral response monitoring.
Two Sentinel-2 and 3 units each are currently flying, with the A units achieving 5 years of operation. The purpose of this presentation is to draw some conclusions from the flight experience and provide recommendations for the future. This activity is performed in the frame of the Copernicus Cal/Val Solution project, which aims at a holistic solution for the calibration and validation of present and future Sentinel missions.
For both OLCI and MSI, the on-board dffusers have proved a reliable and efficient calibration source. No operational issue was encountered, and the diffusers seem remarkably stable over 5 years. However some limitations have been observed. First, inaccuracies in the BRDF characterization lead to seaonnal artifacts on the absolute and relative (in the field) gains.
The second point concers the existence of radiometric biases between the different satellites although they share a common calibration approach. This is even the case for satellites of the same family (2.5% radiometric bias between OLCI-A and B, 1% between MSI-A and B). Although these biases are not very large, they point to a room for improvement in the characterization of the diffuser and the verification of the global uncertainty budget.
The presentation will also address lessons learned from other calibration techniques (dark and spectral). We conclude with some recommendations for future Sentinel missions:
* the characterization of the diffuser should be imporved and made more traceable.
* an in-flight characterization of the BRDF (using satellite yaw manoeuvres) shall be performed during commissioning operations
* the global uncertainty budget for the diffuser should be established according to common standards, and be made available to cal/val users.
This project has received funding from the European Union’s Horizon 2020 research and innovation programe under the grant agreement No 101004242.
Lessons Learned from Operation of On On-Board Calibration Devices on Sentinel Sentinel-2 MSI and Sentinel Sentinel-3 OLCI
Sentinel-2 MSI and Senitnel-3 OLCI are two visible imagers contributing to the European Copernicus Earth Observation program. Both instruments are periodically calibrated using on-board Sun diffusers. OLCI has two Sun diffusers (nominal and reference diffuser), while MSI has only one. OLCI uses a shutter to perform dark signal calibration, while MSI relies on nigtht-time acquisitions over the Ocean. Finally, OLCI has a coloured diffuser for spectral response monitoring.
Two Sentinel-2 and 3 units each are currently flying, with the A units achieving 5 years of operation. The purpose of this presentation is to draw some conclusions from the flight experience and provide recommendations for the future. This activity is performed in the frame of the Copernicus Cal/Val Solution project, which aims at a holistic solution for the calibration and validation of present and future Sentinel missions.
For both OLCI and MSI, the on-board dffusers have proved a reliable and efficient calibration source. No operational issue was encountered, and the diffusers seem remarkably stable over 5 years. However some limitations have been observed. First, inaccuracies in the BRDF characterization lead to seaonnal artifacts on the absolute and relative (in the field) gains.
The second point concers the existence of radiometric biases between the different satellites although they share a common calibration approach. This is even the case for satellites of the same family (2.5% radiometric bias between OLCI-A and B, 1% between MSI-A and B). Although these biases are not very large, they point to a room for improvement in the characterization of the diffuser and the verification of the global uncertainty budget.
The presentation will also address lessons learned from other calibration techniques (dark and spectral). We conclude with some recommendations for future Sentinel missions:
* the characterization of the diffuser should be imporved and made more traceable.
* an in-flight characterization of the BRDF (using satellite yaw manoeuvres) shall be performed during commissioning operations
* the global uncertainty budget for the diffuser should be established according to common standards, and be made available to cal/val users.
This project has received funding from the European Union’s Horizon 2020 research and innovation programe under the grant agreement No 101004242.